1. Field of the Invention
The subject invention relates generally to mechanisms for adjusting the shape of a backrest for seats, and more particularly mechanisms with adjustable lumbar assemblies in seats that conform more closely to the curvature of the human spine to support the back while a person is seated in the seat.
2. Description of the Prior Art
Mechanisms insertable into a backrest of a seat to adjust shape and provide better lumbar support are known in the art. Examples are found in U.S. Pat. Nos. 5,050,930 and 5,397,164 to Schuster et al.
Prior art mechanisms comprise a lumbar support member, commonly referred to as a xe2x80x9clumbar basketxe2x80x9d or xe2x80x9cbasketxe2x80x9d, which is mounted for displacement along a guide track. The lumbar basket may have various configurations. A basic construction involves a pair of brackets displaceable along an axis of the guide track, resilient axial ribs joining the brackets, and resilient transverse ribs fixed centrally to the axial ribs with free ends extending laterally to either side of the axial ribs to provide a cushioning effect. Various mechanisms can be used to draw the brackets together in order to flex the lumbar basket from a relative flat rest state to various bowed states. Various mechanisms can also be used to displace the lumbar basket axially along the track. Thus, the curvature of the lumbar basket and its position within a backrest can be adjusted to provide greater comfort.
The basic lumbar basket described above has a flexed profile which is essentially a segment of a circle, and consequently does not conform adequately to the curvature of a user""s spine. A prior art approach to altering the flexed profile involves fixing a partial central rib to an upper bracket and an upper set of the transverse ribs, making the upper end of the basket more rigid. This induces greater flexing of the basket proximate to the lower bracket, providing greater comfort for many users. There are, however, shortcomings to such an approach. Making the partial rib and then fastening it to multiple components of the basic lumbar basket contributes to cost. There is also little freedom to specify the profile ultimately presented by the basket. Various alternatives can be envisaged to produce baskets that flex to various profiles; however, the basic prior art lumbar basket is simple, and it would be desirable to avoid introducing components and manufacturing steps.
An adjustable lumbar assembly for a seat is disclosed comprising a support, a curved lumbar support member that is movably supported by the support for movement between various degrees of curvature, and an adjustment mechanism operatively connected to the curved lumbar support member for adjusting between various degrees of curvature. The curved lumbar support member consists of a plastic material and includes a plurality of reinforcing ribs that are integral with the curved lumbar support member to allow a greater degree of curvature adjacent one end of the support member than the degree of curvature adjacent the other end of the support member.
Therefore, this invention overcomes many of the disadvantages of the prior art designs since no additional components are needed to alter the shape of the curved lumbar support member. The design of this invention is less expensive to manufacture since no additional components need to be manufactured. Fewer people are needed to assemble the assembly since no additional components need to be added. Further, the weight of the seat is reduced since the curved lumbar support member is made from plastic.